Telegraph signaling system



Dec. 2, 1941. J.vw. COX

TELEGRAPH SIGNALING SYSTEM Filed June 6, 1939 3 Sheets-Sheet l VINVENTOR. JOHN 7725M ATTORNEY Dec. 2, 1941. J. w. cox

TELEGRAPH SIGNALING SYSTEM Filed June 6, 1939 3 Sheets-Sheet 2 5 4INVENTOR. I jmv M 60X BY. 7%

w m A Dec. 2, 1941. J. w. cox

TELEGRAPH SIGNALING SYSTEM Filed June 6, 1939 3 Sheets-Sheet 3 Q W I K.QukVQQQRW ATTORNEY.

Patented Dec. 2, 1941 TELEGRAPH SIGNALING. SXSTEM:

John W. Cox, Berkeley, Calif., 'assignor to Radio Corporation ofAmerica, a corporation of Delaware Application-June 6, 1939, SerialNo..2!7 7,607

6Claims. v (Cl. 250-9) i cxpensive and the maintenance costs are; quitematerial.

It is:one obiect of my invention to devise a telegraph system formultiplex telegraphy that requires no synchronously running distributorsat the transmitter and receiver.

Another object of the invention is to send messages byperiodicallyinterrupting the carrier Wave by low 1 frequencyalternations.

Another object ofthe invention is to simultaneously transmit apluralityof signal messages by interrupting a carrier .wave to form markand space. indications for each message andinterruptingv the markindicationsfor each signal at apredeterminedlow frequency, thefrequencies of interruption being. different for eachsignal message.

Another object of the inventionis to transmit a pluralityof 'messageswithmark and space interruptionscof a carrier wave in whichthemarkingparts of the wave areinterrupted at a plurality ofpredetermined low frequencies and separating... the signal currents ofthe messages at the receiver by filtering.

Another object is. to transmit a .plurality of signal 'messages eachacting on thesame carrier wave toform mark and space interruptions inwhich themarking Wave for each signal message is interrupted'atapredetermined low frequency, the interrupting frequencie beingdifferent for eachsignal message.

Another'object is to'transmit a plurality of signal-messageseachalternately acting on the sameca-rrier'wave --to form mark 'and'spaceindications andinterrupting the marking portions of the wave atpredetermined frequencies, there being-a diiferent frequency for eachsignal message and separating the signal messages by filters at thereceiver.

Another'object of the invention is to assign a carrierwave successivelytoeach of a plurality of transmitting channelsand transmitting mark andspace indications in the carrier wave while 55 interrupting. themarking; portion'of the wave at apredetermined low frequency thefrequency of interruptions being different for each chann91.

Otherobjects will appear in the following. descriptiom. referencebeinghad to the drawings, in which:

Figil is one form: of transmission system. for carrying out myinvention. g t Fig. 2 is a modified form of transmissionrsys- Fig;3.,is;a receiving system; for carrying out my'in-vention.

Fig. 4 is a series'of 'graphs showing a portion .of the carrierwaveformaking the indications.v

Referring to Fig. 1, thelowfrequency oscillator consists of a condenserl havingone terminal connected to the negativeterminal of a battery2.-'a'nd:the other one. connected to two adjustable resistances, 3'and 4which are joined .to live'contacts 5 and 6 of well known perforated tapetransmitters generally indicated at land 8. The tongue -9 of tapetransmitter l is connected to segment. ID of a distributor or commutatorH haying rotating brush I2; The brush l3 of this distributor isadjustably connected to potentiometer I4, l4, connected across battery2; The tongue. l5" of relay 8 is connected to the remaining segment I 6of the distributor; The distributor may be run at any desired speed bymotor I! but it should have a frequency of interruption materially lessthan the frequency of the oscillations produced by the condenser l. Avacuum tube-type of distributor such as the multi-vibrator described'inpatent to R. E. Mathes, No.

1,979,484, November 6, 1934, could also be used, as the invention is notdependent upon any particular type.

Neon or equivalenttube l8 is connected across condenser I throughprimary [9 of a transformer having secondary 20 connected to appropriateamplifiers 2!. The output lines ofthe amplifier are connectedtotransformer 22 feeding the tone keyer stage 23. The secondary of thistransformer is connected'between the grid 24 and filament 25 through'anegative bias 2B. The value of this bias is such that the tube-isblocked except during the positive alternation of the oscillationsproduced by the oscillating condenser I, as hereinafter described.

The plate 21 of the tone keyer stage 23 is coupled to transmitting keyer28 through adjustable resistance 30 connected to positive terminal 3!;Tube'28 is blocked when-tube 23 conducts and it passes current when tube23 is blocked. The plate 34 of keying stage 28 is connected to one endof resistance 35, the other end of the resistance being connected topositive terminal 36. The first mentioned end of resistance 35 isconnected to the primary 3'! of a radio frequency transformer and theother end of this primary is connected to the plate 38 of modulator tube39. The radio frequency oscillator 40 is connected between the grid 4|and filament 42 of tube 39 and the filament is connected to the negativeterminal. The secondary 45 of the output transformer of tube 39 isconnected to appropriate power amplifiers 46 and the output of theamplifiers is connected to an appropriate antenna 4'! and to ground.

The amplifiers 2| and 46 and the oscillator 40 may be of any type wellknown in the art and are therefore shown only in block diagram.

In the modified form of transmitting system shown in Fig. 2, I haveomitted the distributor II and the perforated tape transmitter 'l and 8are connected to individual oscillating condensers with their respectiveneon tubes l8. Devices similar to those of Fig. 1 have been givensimilar reference characters, so they need not be described in detail.The outputs of the oscillators [8 are connected through apparatus to andincluding the antenna that is exactly the same as shown in Fig. 1 andhence it has not been illustrated.

In the receiving circuit shown in Fig. 3 one antenna may be used but onaccount of general fading usually met with in radio systems, I prefer touse the diversity receiving antenna well known in the art and describedin the patent of H. H. Beverage, No. 1,874,866, August 30, 1932. Thismay be generally described as consisting of three antennas 48, connectedto three receivers 49, which may have well known receiving apparatusconsisting of radio frequency tuning stages, heterodyne oscillators,intermediate frequency tuning stages and detectors which are well knownin the art and hence have not been specifically illustrated. Thereceiving apparatus 49 is connected to appropriate amplifiers 59 and theamplifiers are connected to current or voltage limiters to furtherovercome the effects of fading. The limiters of the three circuits ofthe diversity receiving system are all similar and a description of oneis sufficient. In the limiter, the grid 52 is connected through anegative bias of sufiicient value to cut off the desired part of thenegative Wave in the limiting action. Resistance 54 in the plate circuitof this limiting tubeis of such value as to cut a similar part of thepositive half cycle due to electron saturation efiects in the tube.

The output of each limiter is connected to mixing tubes 55 which may bethe same in each of the three circuits. Each mixing tube has a negativebias 56 of such value as to block the tube for the negative half of thelow frequency cycles of the condenser-neon tube oscillator and thuspermit the passage only of the positive cycles. This preventscancellation due to any difference in phase conditions of the currentsin the three circuits and permits proper summation of the signals.

The plates 51 of the mixing or combining tubes are connected in parallelthrough the primary of a transformer 58 to positive terminal 59 andadjustable resistance 60 may be connected in this lead for obtaining theproper plate potential. The secondary of transformer 58 is connected inparallel to two limiters 6i and 6| and the output of each limiter isconnected to band pass filters 63 and 63, one of these filters, say 63,being adjusted to pass one of the low frequencies, say, that controlledby perforated tape transmitter I, and the other one, 63' being adjustedto pass the low frequency controlled by the other perforated tapetransmitter 8. The output of the band pass filter 63 feeds intorectifier 64 and the rectified output passes through smoothing filter 65and is impressed across the grid filament circuit of coupling tube 66.

The output of the band pass filter 63 passes similarly through rectifier54, smoothing filter and coupling tube 65. The output of coupling tubes66 and 66' feed into a signal regenerating circuit shown as the wellknown locking circuit 51, 61' of the patent to Finch, No. 1,844,- 950,February 16, 1932. The regenerated signals from the locking circuitspass into utilization devices such as recorders 68 and 68' of any kind.

The limiters BI and El may be like the limiters 5| or they may be of anyother type. The band pass filters 63, B3, are well known in the art andneed not be illustrated or described except to say that it is preferableto design these filters with a narrow, band width to pass the frequencyinitiated by one perforated tape transmitter and exclude that of theother. The rectifiers 64, 64' may be of the usual vacuum type, or anyother type.

The operation is as follows:

Referring to Fig. 1 when tongue 9 is brought into engagement withcontact 5 by the perforated tape mechanism, condenser I charges bycurrent passing from the positive terminal of the battery throughresistance l4, to brushes [3 and [2, the latter being assumed to be inengagement with segment Ill. The current then passes through tongue 9,contact 5, resistance 3, condenser I, and back to the negative terminalof the battery. As the condenser charges, its voltage increases andfinally the potential is sufiicient to discharge across neon tube l8through transformer coil [9 after which it recharges. The time constantof the condenser l and circuit may be made anything desired by adjustingresistances 3 and I4, but for purpose of explanation and illustration itwill be assumed to be such as to produce a frequency of 500 cycles persecond. Assuming that distributor I2 is run at say, 60 cycles, the brushI 2 will be in engagement with segment in for a sufiicient length oftime to permit the condenser-neon tube oscillator to produce a pluralityof cycles at the frequency of h of 500 cycles per second. The secondary20 of the transformer connected in the circuit of the neon tube I8 willtherefore feed the low'frequency oscillations into the amplifiers 2| andthen into the vacuum tube stage 23, which in this case has sufficientnegative bias to block the plate current on the negative half cycle.

The fiow of plate current in tube 23, when a positive half cycle voltageis impressed across the input circuit, places such a heavy drop inresistance 30 that tube 28 is blocked by the negative voltage. Therebeing no plate current in tube 28 during this positive half wave of thevoltage wave initiated by perforated tape transmitter I, the drop inresistance 35 produced thereby is removed and tube 39 passes currentunder influence of the radio frequency impressed across its input byoscillator 49. A radio frequency wave is thus radiated from antenna 41during the time of this low frequency half cycle. This is indie 39:vbeing. virtually short-circuited. Therefore,

during the negative half cycle there is no radiation from'antennar l'l,as indicated at 10 in Fig. .4.

Since the frequency of the. condenser-neon tube oscillator isconsiderably higherv thanthe frequency of interruption by distributorII, a number of groups-of highfrequency waves-69, H, 12, will beradiated before brush1.l0- leaves, segment l0. When the brush leavesthis segment and engages contact I6, condenser I and circuit then hasanother time constant by virtue of the substitution ofresistanceA forresistance 3 and another low frequency, 1000 cycles, per second, forexample, is produced. by the. condenser-neon oscillator in secondary andthe radio frequency carrier of oscillator isradiated from antenna M in anumberof groups starting at 13. These groups have" the frequency f2 or1000 in the example given. In thisway the perforated tape transmitters 1and 8 will cause alternate groups of radio frequency waves to beradiated, the one group having a frequency of f1 and the other f2.

The mark indications of the two transmitters l and 8 may start at anytime as they are independent of each other, but by way of example, Ihave indicateda mark for transmitter 1 as starting with group 69- andending with group 14. Similarly themarkfor transmitter 8 is illustratedas commencing with group 13 and ending with group 16. Graph A is brokenaway at H to indicate that there are more groups. for the marks than canbe shown in the drawings with a suitable scale.

The radiated wavesare-received and detected at 19 and amplified at 5B inall three of the channels in the diversity receiver. The amplified audiocurrents are then limited at 5| to cut off the desired amount of thepositive and negative cycles to reduce fading effects. The output of thethree limiters are mixed in the plate circuits of the rectifiers andintroduced into the two channels through limiters 6|, 6|. Band passfilter 63 passes the low frequency alternations f1 and excludes f2 whileband pass filter 53' passes f2 and excludes f1. lated and when rectifiedat 64, 64 will appear as indicated by the dotted line 15 in graph B. Atthis point the voltage will have positive pulses of frequency f1, brokenup at the lower frequency of the distributor I l. However, when thevoltage passes through the smoothing filter 65 it will be smoothed outas indicated by line 13. Similarly the rectified voltage of frequency f2and the smoothed out voltage will be indicated by M and respectively, ofgraph G, which indicate the marks of the respective signals. The spacesof these signals are caused by the tube 28 normally shorting the platevoltage of amplifier 39 when no signals are being sent out by tapetransmitters i and 8.

The signals after being rectified could be used to operate the recorders68, 58, directly but it is preferable to square up the marks by aregenerating device such as the locking circuits 67, 61. Referring tograph B, when the voltage 13' is The two signals are thus isoapplied to.tube-fifirit produces a drop in resistance 16 by the. plate; current andcondenser 16, previously charged toifulljline voltage, dischargesthrough the platezfilament circuit of tube 66 to the center of--the.battery Hf, through one-halfof the battery and resistance 18 tothe other side of the condenser: The drop in resistance 18 places aheavy biasonthegrid of tube-19 and blocks the tube. Tube 86 was,previously blocked by the drop; in resistance -8-l caused by the platecurrent of tube l9'.and when'it is removed the voltage of the grid:oftube 8.0 rises to full positive value. Tube-8ii-then draws. platecurrent and instantly blocks tube-J9 by; theinegative drop applied toits grid by resistance 82.v This happens at a predei terminedvalue'ofthe, signal voltage, say that indicated at the point 83 of graph B. Thevoltage: across lines-8G, 85, of the recorder, rising instantly to thevalue. 86 in graph B, will remain constant until the balance of thelocking circuit is; disturbed by the decrease of the'sign-al to apredetermined value 81. It will be noted that at this time outputline844s positive and line is negative.

When .point 87 in. the voltage curve 13 is reached, the chargingcu-rrentthrough condenser 7%., due to decrease of drop. in resistance 76,becomes heavy enough to place-a .suflicient positive drop in the grid oftube. 79, to cause that tube to conduct current. Thisinstantly causestube 88 to block due-to the negative voltage placed on its grid due. tothe-drop in resistance 8|. The voltage acrosslinestt and BEimmediatelyreverses at point .87 and the space fiaistarts to form. This space willcontinue until the beginning of another mark starts to fornnwhereuponthe balance will be again disturbed by the condenser again discharging,it havingbeen charged to fu1lbatteryvoltage while the space was beingformed.

The signal initiatedby tape transmitter 8 after the, currentv passesthrough smoothing filter E6 will operate locking circuit 61" in exactlythe same way locking circuit 6'! was operated and the final squaresignal wave at the input terminals of recorder 58" will be as indicatedby 89, 96, of graph C. No distributorisrequired at the receiver andhence synchronization between transmitter and receiver is entirelyabsent.

In the modified transmitting system of Fig. 2 the distributor ll of Fig.1 has been omitted and two condenser-neon tube oscillators have beenused. Condenser l of the respective channels will each oscillate at alow frequency depending upon the constantsof the circuit as in Fig. 2.The tape transmitters 1 and B will cause these oscillators to generatealternating voltage each time a marking contact is made. Eachoscillating circuit is independent of the other and the low frequencyoutput of the secondaries 20 are superposed on each other, and fromthere on the circuit to and including the antenna will be as describedin connection with the apparatus of Fig. 1 except for the interrupterII. The receiving operation will also be as described in connection withFig. 3 with a similar exception in respect to the interruption of thedistributor Ii which will be absent. The modified form in Fig. 2 will besatisfactory but it is not preferred because the signal of one channelmodulates the signal of the other by interaction. However, there willremain sufficient pulses at the band pass filters to enable the latterto separate the signals at the receiver and they will produce a suitablerecord.

In both forms of transmitting systems I may use any kind of lowfrequency oscillator, the one disclosed being by way of example only.Various other modifications may be made without departing from thespirit of the invention.

Having described my invention, what I claim 1. In multiplex radiotelegraphy, a generator of high frequency oscillation, means forgenerating a plurality of alternating electromotive forces each having adifferent low frequency, signal transmitting devices each having meansto send mark and space signals by interrupting current from thefirst-mentioned means for one of a plurality of messages, means forrectifying the interrupted currents of the generating means, adistributor connected to the signal transmitting devices forinterrupting the signals therefrom at a frequency below the frequency ofthe low frequency generating means, and means for transmitting said highfrequency oscillations only during the time periods of the currentpulses in said rectified currents.

2. In multiplex radio telegraphy, an antenna, a generator of highfrequency oscillations, means for generating a plurality of alternatingelectromotive forces each having a difierent low frequency, signaltransmitting devices each having means to send mark and space signals byinterrupting current from the first-mentioned means for one of aplurality of messages, a distributor connected to the signaltransmitting devices for interrupting the current therefrom at afrequency below the frequency of the low frequency generating means,means for rectifying the output of the generating means, and means forpassing the high frequency oscillations to the antenna only during thetime periods of the pulses in said rectified current.

3. In signaling systems having a plurality of channels, a high frequencyoscillator, means for producing a plurality of currents of different lowfrequency, means for modulating each current in accordance with amessage, a rectifier, means to pass the modulated low frequency currentsto the rectifier in timed succession for a uniform time intervalmaterially longer than the periodic time of the lowest frequency of thefirst-mentioned means, and means for modulating the high frequencyoscillator by the rectified low frequency currents.

4. In signaling systems having a plurality of channels, a high frequencyoscillator, means for producing a plurality of low frequency currents,means for rectifying the low frequency currents, means for modulatingthe high frequency oscillator successively by each of the rectified lowfrequency currents during an interval of time greater than the periodictimes of the frequencies, and means for interrupting the low frequencycurrents to form mark and space signals of materially greater timelength than said time intervals.

5. In signaling systems having a plurality of channels, a high frequencyoscillator, means for producing in each channel current of a lowfrequency differing from the frequency of the other current. means tointerrupt each low frequency current to form mark and space signals, arectifier, means to pass each interrupted low frequency current insuccession to said rectifier for uniform periods of time materiallylonger than the periodic time of any of said low frequencies and shorterthan the time length of the shortest signal, and means for modulatingthe high frequency oscillator by the rectified low frequency currents.

6. In signaling systems having a plurality of channels, a high frequencyoscillator, means for producing in each channel current of a lowfrequency differing from the frequency of the other current, a modulatorconnected to said oscillator, means to pass each low frequency currentin succession to said modulator for uniform periods of time materiallylonger than the periodic time of any of said low frequencies and shorterthan the shortest signal, and means to interrupt each low frequencycurrent to form mark and space signals, said modulator having means forcausing said oscillator to oscillate only during alternate half cyclesof said low frequencies.

JOHN W. COX.

